sharkbait Posted January 12, 2012 Report Share Posted January 12, 2012 I'm pretty rubbish with Carbs so need some pointers here. My '97 315 (with PHBH carb) is quite jerky at low revs - so if I'm moving slowly the bike will keep jumping forwards a little. Air screw is currently 1.5 turns out. On more open throttle it seems better. I've taken the carb off and cleaned it but may have missed something. I checked 3 jets (main, the short idle jet and the one up inside the 'tube') which looked OK. I did notice that one of the floats has some rub marks on it - no idea how it could have got these but they're there. Also the slide has some wear marks on the side, could these be the issue? Is it worth repairing or would I be better of trying to find a used PHBL? Quote Link to comment Share on other sites More sharing options...
canada280i Posted January 12, 2012 Report Share Posted January 12, 2012 If you have cleaned the carb and jets etc. you may want to take a look at the reeds just to make sure they are not cracked or chipped and to make sure they are seating correctly against the reed block. Quote Link to comment Share on other sites More sharing options...
sharkbait Posted January 12, 2012 Author Report Share Posted January 12, 2012 If you have cleaned the carb and jets etc. you may want to take a look at the reeds just to make sure they are not cracked or chipped and to make sure they are seating correctly against the reed block. Right... I've got looked at those at all. Would they cause a lumpy bottom end (missus)? Quote Link to comment Share on other sites More sharing options...
canada280i Posted January 12, 2012 Report Share Posted January 12, 2012 maybe, if they are not sealing correctly to the reed block it may allow the engine to run on a little resulting in some jerk as the engine is fed off-throttle. I'm no expert but did experience something similar when evaluating stock reeds versus boyesens, I put the stock reeds back in and over tightened the reed stop resulting in one of the reeds not sealing correctly and it was almost like the engine was constantly overrevving jsut a little. When I ultimately put the boyesens back in I was careful to make sure they were a snug seal against the reed block. Quote Link to comment Share on other sites More sharing options...
clay Posted January 12, 2012 Report Share Posted January 12, 2012 (edited) Hi bud, my mixture screw is more towards (two + half) turns out? what colour is the plug? Edited January 12, 2012 by clay Quote Link to comment Share on other sites More sharing options...
totalshell Posted January 12, 2012 Report Share Posted January 12, 2012 clean the carb out and use an air gun or canned air through all the jets etc clean the airfilter and oil it clean the airbox and the pipework connecting it to the carb. replace the fuel filter. you could spend as much as 4 quid and an hour doing that lot. run the bike get it nice and warm, get it on a nice flat piece of land car park etc. the bike should run 'fairly' smoothly in first gear with no throttle getting that zero throttle run as smooth as possible is the aim use the air/ petrol screw and the tickover screw to achieve this start with the air/ petrol screw 1.5 turns out and raise the tickover so that the bike fast idles turning the air/ petrol screw should make it run fast one way and slow the other get it to where it runs faster and turn the tickover screw out the bike should run slower as it runs more on the pilot jet. getting this sweet spot could take a little while of experimenting but only try one screw at a time and remember where it was before you started.. do half turns then qtr the eight till your on the money.. patience is your friend.. Quote Link to comment Share on other sites More sharing options...
sharkbait Posted January 12, 2012 Author Report Share Posted January 12, 2012 clean the carb out and use an air gun or canned air through all the jets etc clean the airfilter and oil it clean the airbox and the pipework connecting it to the carb. replace the fuel filter. you could spend as much as 4 quid and an hour doing that lot. run the bike get it nice and warm, get it on a nice flat piece of land car park etc. the bike should run 'fairly' smoothly in first gear with no throttle getting that zero throttle run as smooth as possible is the aim use the air/ petrol screw and the tickover screw to achieve this start with the air/ petrol screw 1.5 turns out and raise the tickover so that the bike fast idles turning the air/ petrol screw should make it run fast one way and slow the other get it to where it runs faster and turn the tickover screw out the bike should run slower as it runs more on the pilot jet. getting this sweet spot could take a little while of experimenting but only try one screw at a time and remember where it was before you started.. do half turns then qtr the eight till your on the money.. patience is your friend.. Brilliant, thanks TS - great info and certainly the path I'll be taking I owe you one of these Quote Link to comment Share on other sites More sharing options...
sharkbait Posted January 12, 2012 Author Report Share Posted January 12, 2012 Hi bud, my air mix is more towards two + 1/2 turns out? what colour is the plug? Not bad, could be browner. Does the airscrew out make it leaner or richer? Quote Link to comment Share on other sites More sharing options...
wherry Posted January 12, 2012 Report Share Posted January 12, 2012 Does the airscrew out make it leaner or richer? On the PHBH the mixture screw works on the air circuit so out = leaner (more air). Quote Link to comment Share on other sites More sharing options...
sharkbait Posted January 12, 2012 Author Report Share Posted January 12, 2012 On the PHBH the mixture screw works on the air circuit so out = leaner (more air). Cheers Wherry. When I got the bike it was 1.75 turns out so probably too rich. Quote Link to comment Share on other sites More sharing options...
sharkbait Posted January 14, 2012 Author Report Share Posted January 14, 2012 Cheers Wherry. When I got the bike it was 1.75 turns out so probably too rich. Had a good go at the carb today. Cleaned it again and found the hidden jet underneath the pilot jet and it looked a bit blocked. Running better now, may do some more playing tomorrow. oh yeah, i tried running the bike without the 'hidden' jet and it was very rich, so I put it back. New plug arrives on monday so that may also help. Quote Link to comment Share on other sites More sharing options...
nelly1 Posted January 14, 2012 Report Share Posted January 14, 2012 i run an iridium plug in mine it rins great with it Quote Link to comment Share on other sites More sharing options...
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